Exemplary embodiments of the present invention relate to a device for inflating an at least two-layered air bag folded to form an inflatable belt for a safety system of a motor vehicle equipped with a gas generator.
Air bags are typically located in the steering wheel, in the instrument panel in front of the passenger, laterally on the B-post, below the steering wheel or in the seat and are inflated in an accident. The purpose of the air bags is to prevent the vehicle occupant from hitting the vehicle structure or hard parts of the vehicle, such as the steering wheel or the windshield, during the accident and is seriously injured. The inflated air bags can also alter the sequence of movements of the occupant in the course of his/her forward displacement, thereby, for example, avoiding the dipping or sliding through or under the seat belt which is known as “submarining”. Such inflated air bags are further used as inflatable seat belts that are folded to form a belt and wound onto a belt retractor.
In order to inflate the air bags it is common to use gas generators connected to the air bag by a connecting piece. The gas stream generated by the gas generators is, for example, fed into the air bag via a gas passage, and additional gas lances may be provided to distribute the gas stream in the interior of the air bag.
European Patent Document EP 1 347 894 B1 discloses an air bag that is inflated via an inflation unit provided with a nozzle head. The inflation unit is connected to the air bag via the nozzle head in a gas-tight manner, for which purpose a connecting piece specifically adapted to the air bag and a corresponding design of the connecting region of the air bag itself are required.
Inflatable belts are basically subject to the problem of deciding at which point the gas generator is connected to the inflatable belt, because the belt is subject to repeated extraction and retraction movements. For this reason, inflatable belts are usually filled from the end fitting. Otherwise, a very complex filling operation via the belt latch is required.
European Patent Document EP 1 056 894 B1 discloses a two-layered inflatable single-part belt webbing, in particular for a seat belt, which is woven as a tubular belt webbing.
German Patent Document DE 10 2008 048 340 B3 describes a device for inflating an at least two-layered air bag for a safety system of a motor vehicle equipped with a gas generator. The gas stream generated by the gas generator is directed onto the air bag from the outside. By means of the gas stream, an opening can be burned into at least one of the layers of the air bag. In one embodiment, the gas stream has a temperature of at least 600 degrees.
The burning of the opening into the airbag is a chemical reaction that requires, in addition to a combustible material, an oxidant such as oxygen, with which the combustible material forms a chemical compound in the burning process, which is also known as combustion. To start the reaction, which then runs while giving off energy, an activating energy is required. Burning an opening into the airbag requires both a sufficient quantity of oxidant and a sufficiently high activating energy for starting the reaction, for example in the form of a correspondingly high temperature. The required activating energy depends, among other factors, on the combustible material. If even one of these preconditions is not met, it is not possible to burn an opening into the airbag.
To protect the occupant secured by the air bag against higher temperatures of the gas stream fed into the air bag, suitable protective measures are required, for example a sufficiently thick cover for the air bag, so that the temperature at the outside of the cover facing the occupant is tolerable for the occupant after the air bag has been inflated. The higher the temperature of the gas stream, the more complex such protective measures will be.
Exemplary embodiments of the present invention are directed to the problem of improving a device for inflating a two-layered air bag folded to form an inflatable belt.
In accordance with the present invention the gas stream generated by the gas generator is directed onto the air bag from the outside and the gas stream produces an opening in at least one of the layers of the air bag in a physical process.
The opening is, for example, produced by an at least partial melting or tearing of at least one of the layers of the air bag in a region to which the gas stream is applied. Several physical processes can be combined to produce the opening. The material of the air bag can, for example, be melted by a gas stream temperature above the melting point of the material, and this melt can be blown away by the gas stream itself. In a material commonly used for an air bag or for a belt webbing, the melting point is significantly below an activating energy required for burning the material. The material can, for example, be torn by the kinetic energy of the gas stream. The material of the air bag can also be softened or weakened by a gas stream temperature that is below its melting point but above ambient temperature, making it easier to tear the material.
Producing an opening in the air bag in a physical process offers several advantages compared to burning an opening. The physical process does not require an oxidant such as oxygen, which has to be available in sufficient quantities for burning in the gas stream or in its immediate surroundings. Further, there is no need to exceed an activating energy for the physical process, which allows the gas stream to have a lower temperature. As a result, the measures to protect the occupant secured by the air bag against the temperature of the gas stream fed into the air bag can be made less complex.
It was surprisingly found that the air bag even unfolds if the gas stream is directly oriented onto the air bag from the outside, so that no connecting ports or connecting pieces are required. The gas stream is then directly fed through the layer of the air bag that is subjected to the gas stream, the introduction of the gas stream being facilitated by an opening produced by the gas stream in at least one of the layers of the air bag.
In accordance with the present invention the direction of the gas stream and the unfolding direction of the air bag as provided enclose an angle of less than 90 degrees. In this way, the orientation of the gas stream already determines the unfolding direction, and the inflation of the air bag is accelerated. This further produces an undulation in the layer exposed to the gas stream, so that this layer is subjected to an additional mechanical stress and the production of the opening is accelerated further.
In an advantageous embodiment, the air bag is designed as an inflatable belt in such a way that it at least partially meets the requirements of a belt webbing of a seat belt for protecting vehicle occupants, in particular in terms of tear resistance and expandability. An example for such belt webbing is described in European Patent Document EP 1 056 894 B1.
In order to avoid damage to adjacent parts in the motor vehicle by the gas stream and in order to use the gas stream optimally for inflating the air bag, a housing encapsulates the region of the air bag onto which the gas stream is directed, the gas stream and at least the region of the gas generator where the gas stream emerges.
The gas generator can be arranged opposite the air bag without touching it. In this way, the air bag is only loaded by the impinging gas stream, and the emerging gas stream can develop before hitting the layer of the air bag, so that it has the necessary thermal and kinetic energy for producing the opening. The phrase “without touching” should be understood in this context to mean that there is no contact between the gas outlet surface of the gas generator and the air bag, but the housing of the gas generator may of course be in contact with the air bag.
Due to the device according to the invention, the belt can now be filled at any point, for example at an exit point from a belt retractor.
The device can comprise a guide for the belt, so that the relative arrangement of individual components, and in particular the distance of the belt from the gas generator, remains unchanged even while the belt is retracted or extracted.
In one embodiment, the belt is blocked in the direction of belt extraction at the time when the gas generator is ignited. This prevents any movement of the belt in the direction of belt extraction that may be caused by the impinging gas stream and thus any movement of the point on the belt that is hit by the gas stream.